In recent years, attention has been paid to a ferromagnetic dielectrics (multiferroics) material which simultaneously has ferromagnetism and ferroelectricity and which exhibits a composite function, and research and development on this material has been aggressively carried out.
This ferromagnetic dielectric material has been known as a material having a so-called magnetoelectric effect in which when a magnetic field is applied, by induction of spiral magnetic ordering, the ferroelectricity is exhibited, so that the electric polarization is generated, or the electric polarization and/or the dielectric constant is changed, and in which when an electric field is applied, the magnetization is generated or is changed.
Since the ferromagnetic dielectric material can generate by the magnetoelectric effect described above, the change in magnetization by application of an electric field and the change in electric polarization by application of a magnetic field, this ferromagnetic dielectric material is expected to be applied to various ceramic electronic components, such as a variable inductor in which the magnetization is changed by application of an electric field, a variable magnetic device for a writing head of a memory medium, a magnetic sensor detecting magnetism, and a nonvolatile memory.
In particular, research and development of ferromagnetic dielectric materials exhibiting a “gigantic magnetoelectric effect” in which the electric polarization is significantly changed by application of a magnetic field has been actively carried out.
For example, Patent Document 1 has proposed a multiferroic element in which by application of an external magnetic field to a multiferroic solid material simultaneously having ferroelectricity and ferromagnetism that has a spin structure, the spin direction of which is rotated so as to be along the outer side of a corn (apex angle α of the top of the corn is in a range of 0°<α≤90°, the direction of the electric polarization approximately orthogonal to the external magnetic field described above is controlled.
In this Patent Document 1, by the use of MCr2O4 (M=Mn, Fe, Co, or Ni) as the ferromagnetic dielectric material (multiferroic material), the electric polarization is generated in an ultralow temperature region of approximately 26K by application of a magnetic field, and an electric polarization of 2 μC/m2 is obtained at approximately 5K.
In addition, Patent Document 2 has also proposed a multiferroic element which is formed of a multiferroic solid material containing iron oxide as a primary raw material and simultaneously having ferroelectricity and ferromagnetism and which is designed to induce a current by application of a weak external magnetic field of 300 Gauss or less.
This Patent Document 2 has disclosed that when a ferrite compound of Ba2Mg2Fe12O22 is used as the ferromagnetic dielectric material (multiferroic material), and a low magnetic field of 300 Gauss (0.03 T) is applied thereto, a current flows at −268° C. (5K) corresponding to the application of an alternating magnetic field, and positive and negative electric polarizations are also alternately generated.
In addition, Patent Document 3 has proposed a magnetoelectric effect material which is formed of an oxide ceramic as a primary component represented by a general formula of (Sr1-αBaα)3(Co1-βBβ)2Fe24O41+δ (in the formula, B represents at least one type of element selected from the group consisting of Ni, Zn, Mn, Mg, and Cu, and α, β, and δ satisfy 0≤α≤0.3, 0≤β≤0.3, and −1≤δ≤1, respectively) and which exhibits a magnetoelectric effect in a temperature range of 250K to 350K and a magnetic field range of 0.05 T (tesla) or less.
According to this Patent Document 3, when a ferromagnetic dielectric material having a hexagonal Z-type crystal structure represented by the above general formula is used, and when sweeping is performed in a magnetic field range of −0.05 to +0.05 T, a ferromagnetic dielectric material is obtained which has an electric polarization of 1.0 to 9.5 μC/m2 and a magnetoelectric coupling factor of 100 ps/m to at most 470 ps/m at approximately room temperature and in a magnetic field range of 0.05 T or less.
Patent Document 1: International Publication No. 2007/135817 (claims 1 and 3, Paragraph No. [0031], FIG. 7, and the like)
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2009-224563 (claims 1 and 3, Paragraph No. [0032], FIG. 7, and the like)
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2012-1396 (claim 1, Paragraph Nos. [0010] and [0061], Table 3, FIG. 3, and the like)